1. Field of the Invention:
The present invention relates to a pneumatic twisting spinning apparatus for producing high-quality spun yarn as of natural and synthetic fibers stably at a high speed with a low power requirement.
2. Description of the Prior Art:
Typical known spinning apparatus include ring spinning frames and open-end spinning machines.
The ring spinning frames have found versatile use as it can produce a wide variety of yarns of from low to high yarn number counts. However since they utilize a revolving package, the spinning speed is on the order of 20 m/min., which will be difficult to increase markedly in the future.
The open-end spinning machines, which have been developed recently, are more productive since they operate at speeds two or three times higher than those of the ring spinning frames. The open-end spinning machines, however, are used mainly for forming coarse yarns for the reason that if fine yarns were to be produced on the machines, fibers would be bent into hooks and loops on the yarn formed.
Various bundled-yarn spinning apparatus or pneumatic twisting spinning apparatus have been proposed for producing bundled yarns in which peripheral fibers are wound around central fibers that are substantially untwisted.
The basic principles of such pneumatic twisting spinning apparatus or bundled-yarn spinning apparatus will be described with reference to FIG. 1.
Staple fibers, such as natural and synthetic fibers, known as sliver SL or roving are supplied to a drafting device D in which staple fibers supplied are drafted several ten or hundred times into a bundle S of fibers, or fleece, having a thickness equal to that of a yarn to be produced.
A false twister K rotates the fleece about its own axis until it is twisted. The fleece S as it leaves a front roller assembly FR is twisted by rotation of the false twister K. The false twister K may rotate in a righthand or lefthand direction, and the fleece shown in FIG. 1 is given a Z twist upstream of the false twister K. In FIG. 2(A), assuming that the fleece travels at a speed of v upstream of the false twister K and the false twister K rotates at a speed of n, the fleece is given a twist of n/v. As the fleece goes past the false twister K, or at a position downstream of the false twister K, the fleece is given an S twist which is opposite to and hence untwists the Z twist given upstream of the false twister K. Since the false twister K rotates at the same speed as that of travel of the fleece, the fleece becomes completely untwisted when it reaches a winding roller MR, and no yarn is produced.
In FIG. 2(B), the fleece S as it emerges from the front roller assembly FR is subjected to an apron or an air stream so that the fleece will not wholly be twisted by the false twister K. Central fibers (hereinafter referred to as "main fibers") of the fleece are twisted by the false twister K in a manner described above. Peripheral fibers (hereinafter referred to as "free fibers") remote from the center of the fleece are not twisted for a while after the fleece has left the front roller assembly FR, and start being twisted when they become attached to the main fibers as the fleece approaches the false twister K. Therefore, the free fibers as they are located upstream of the false twister K are given a twist of dn/v (0&lt;d&lt;1) which is smaller than the twist of n/v given to the main fibers. As the fleece thus twisted moves through the false twister K, it is rotated in a direction to have an S twist which is opposite to a Z twist. The twist given upstream of the false twister K is thus gradually untwisted. Between the false twister K and take-up and winding rollers TR, MR, the fleece is given an opposite twist of n/v. The main fibers have no twist as the twist given upstream of the false twister is offset by the twist applied downstream of the false twister. However, the free fibers are given the twist of dn/v upstream of the false twister and the twist of n/v downward of the false twister, where dn&lt;n, a twist of n-dn/v is left in the free fibers. A yarn T produced by a pneumatic twisting spinning apparatus retains its strength due to such twisted free fibers.
Known pneumatic twisting spinning apparatus are disadvantageous in that many yarn breakages occur during spinning, and a yarn strength required in actual use is unavailable. As the apparatus is operated at higher speeds, the behavior of fleece becomes more unstable and it becomes still more unstable as it is disturbed by an air flow caused by the front roller assembly rotating at a high speed. The shorter and fewer the fibers are, the more unstable the fleece becomes, resulting in a tendency to be broken by a slight disturbance which the fleece is subjected to. The conventional apparatus have thus been limited to use with relatively long fibers and with a relatively low spinning speed, and hence have not practically been usable.
Proposals have been made to give bundled yarns an increased strength which the aforesaid apparatus have failed to provide.
One such proposal is to spread and distribute a fleece as it is discharged from a drafting machine. Since this merely serves to produce free fibers, it is only applicable to long fibers in order to form strong yarns stably, and hence is practically unsatisfactory.
Another proposal uses an apron driven by a front roller assembly of a drafting machine. The apron has a poor degree of durability in operation and involves difficulty in maintenance. A recessed roller may be used to grip a fleece softly. It is however quite difficult to provide a suitable degree of softly gripping pressure for producing a bundled yarn of sufficient strength. Such a recessed roller is of little use from the practical standpoint.